Television broadcast system



Sept. 2, 1941. A. v. LOUGHREN TELEVISION BROADCAST SYSTEM 3 Sheets-Sheet1 Filed June 9, 1958 ,INVENTOR ARTHUR V. LOUGHREN W ATTORNEY Sept. 2,1941. A. v. LOUGHREN TELEVISION BROADCAST SYSTEM `s sheets-sheet 2 FiledJune 9, 1938 w. mommw m v.

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Sept. 2, 1941. A. v. I OUGHREN TELEVI S ION BROADCAST SYS`TEM Filed June9, 1958 s sheen-sheet 5 AR HUR V. LOUG REN ATTORNEY Patented Sept. 2,1941 TELEVISION BROADCAST SYSTEM Arthur V. Loughren, Tuckahoe,r N. Y.,assigner to Hazeltine Corporation, a corporation of Dela- WaleApplication June 9, 193s, seria1No.21z,s91

(c1. 17a-6.a)

30 Claims.

'I'his invention relates to television systems and is particularlyconcerned with the provision of an improved type of television signaltogether with transmitting apparatus and receiving apparatus forgenera'ting and utilizing such signal, respectively.

In accordance with present television practice, there is developed andtransmitted a signal which comprises a carrier wave modulated duringsuccessive intervals or trace periods by videosignal componentsrepresentative of the light and shade values of an image beingtransmitted.

During retrace intervals between the trace periods, the carrier wave ismodulated by synchronizing impulses or components which correspond toinitiations of successive lines and elds in the scanning of the image.At the receiver, a beam is so deected as to scan and illuminate a targetin a series of eldsV or parallel lines, the video-signal componentsbeing utilized to control the intensity of the beam. The line-scanningand field-scanning synchronizing components are separated from thevideo-frequency components and from each other and are utilized tosynchronize the operation of the receiver linescanning andfield-scanning apparatus with similar apparatus utilized at thetransmitter in developing the signal. The transmitted program or imageis thereby reconstructed on the target of the receiver.

Various types of television signals, as Well as various types ofscanning and synchronizing methods and apparatus, have been proposed.For example, in certain systems negative modulation is employed, thatis, a decrease in carrier 35 amplitude during the trace periods, whenthe carrier is amplitude-modulated by the videosignal components,corresponds to an increase in amplitude corresponds to an increase inillumination. The synchronizing-modulation components of the signalsused in these systems ordinarily have amplitude values outside the rangeof video-modulation components. Where negative modulation is employed,they are represented by increase in carrier amplitude while, wherepositive modulation is employed, they are represented by decreases incarrier amplitude, in either case usually having amplitude valuescorresponding to blacker-than-black.

In present practice With negative modulation, synchronizing signalsrepresent an increase in transmitted'power of approximately 55% overillumination. In other systems, positive modulation is utilized in whichan increase in carrier ulated or trace portions of the signal. This isundesirable not only because of the uneconomical requirement ofincreased power, but also due to the fact that interference presented bythe signal of one program with another is a function of the peak valueof the power radiation of the signal of the interfering program.

In 'television receiving systems noise components disturb both thevideo-signal and the synchronizing-signal compounds. In general, noiseimpulses are represented by increases in carrier amplitude so that, inpositive modulation systems, the noise components appear in the image aswhite spots while, in negative modulation systems, 'they appear as blackspots. The white spots are usually the more annoying to an observer sothat, as far as the video signal is concerned, a negative modulationsignal is less affected by noise. On the other hand, with negativemodulation the synchronizing components are represented by increases incarrier amplitude and are thus most subject to noise eiects, while withpositive modulation synchronizing components are represented oy areduction of carrier amplitude, usually to zero, so that they aresubstantially less affected by noise. Therefore, as far as thesynchronizing components are concerned, a positive modulation signal isless affected by noise.

It is an object of the present invention, therefore, to provide animproved television system utilizing a carrier wave havingl thedesirable characteristics incident to negative modulation with respectto the video-signal components and including synchronizing componentswhich are not appreciably affected by the effects of noise disturbances.

It is a further object of the invention to provide a system of thecharacter described wherein the carrier wave is negatively modulatedduring trace periods by videcsignal components and is modulated bysuitable synchronizing components during retrace scanning intervalswithout any appreciable increase in the transmitted power over thatrequired for the video-modulation components of the wave.

In accordance with a feature of the present invention, there is provideda television transmitting system comprising means for developing acarrier wave, means for developing videofrequency components duringtrace periods, and means for developing synchronizing-signal ccmponentsduring retrace periods. The system also includes means foramplitude-modulating the the maximum power required for thevideo-modcarrier wave in accordance with signal compomeans fortransmitting the modulated-carrierwave. The carrier wave may, forexample, normally have a predetermined frequency -and be shifted withrespect to this frequency during the retrace scanning periods. Thisfrequency modulation, or shifting of the carrier frequency,corresponding to synchronizing impulses may comprise a single shift perimpulse, it may be for di'erent durations for line-synchronizing andfield-synchronizing impulses,- it may comprise a plurality of successivecyclesof predetermined different periods, or it may comprise anysuitable combination of these characteristics. Also in accordance with afeature of the invention, a station is provided for receiving andreproducing a program transmitted by a carrier wave of the typedeveloped by the transmitter described, this station including means forselectively receiving the carrier wave, means for detecting signalmodulation of one type for deriving the video-'signal components, andmeans for detecting the signal modulation of the other type 'forderiving synchronizing-signal components. Means are provided forutilizing the derived components to reproduce the transmitted program.

Also in accordance with a further feature of the invention, a televisionbroadcast system comprises a transmitter of any of the types 4mentionedabove and a suitable receiving station.

therefor;

In accordance with another Vfeature of the invention, the `transmittingsystem -may be ar-` ranged to transmit only the carrier and that retraceperiods. also the transmitter, then include a band-pass selector fortranslating the carrier and its proper 4 sideband, which selector has aresponse characteristic with a sloping side and a mean frequency sorelated to Vthe predetermined carrier frequency that the latter islocated on the sloping include a cathode-ray signal-generating tube II.having the usual electron gun and photosensitive target andline-scanning and held-scanning elements I Ia and I Ib, respectively.'Ihere arealso provided a line-scanning wave generator I2 and afield-scanning wave generator I3 with theiroutput circuits connecteddirectly to the linescanning elements IIa and field-scanning elementsIIb, respectively. In order to provide pedestal impulses fory blockingout, or for supi pressing undesirable impulses in, and ensuring theproper wave form of, the modulation signal side. By virtue of thisarrangement, there is obtained an effective increase in the amplitude ofthe carrier wave during synchronizing-signal modulation periods withrespect to the videomodulation periods, without the requirement ofincreased power transmission at the transmitter.

For a better understanding of the invention, together with other andfurther objects thereof, reference is had to thefollowing descriptiontaken in connection with the accompanying drawings, and its scope willbe pointed out in the appended claims.

In the accompanying drawings. Figs. 1 and 2 are circuit partiallyschematic, of complete television transmitting and receiving systems,respectively, embodying the present invention; Figs. 2a and 2b arediagrams illustratying modifications of parts of the receiver of Fig.

2; Figs. 3-7, inclusive, are graphs illustrating the wave forms ofsignals developed by the apparatus of the present invention; and Figs.8-10, inclusive, are graphs illustrating certain operatingcharacteristics of the systemsv shown-in Figs. 1

developed by the generator III, there is provided a pedestal-impulsegenerator I4 having its output circuit coupled vto the control grid ofthe signal-generating tube II. synchronizing-signal-generating apparatusis provided in accordance with the present invention and will behereinafter described in detail.

In order to synchronize the operations of the generators I2, I3, and I 4and the synchronizingsignal-generating apparatus, there is provided atiming-impulse generator I 5 having a plurality of output circuitscoupled to the generators I2, I3, and Il and to the units of thesynchronizingsignal-generating apparatus, as presently to be explained.

A- modulation-frequency amplifier I6 is coupled to outputcircuits of thecathode-ray signalgenerating tube II and the pedestal generator Il. Thetransmitter also includes means comprising a local or master oscillatorI8 for generating a signal-carrier-wave and means includ- .ing avideo-frequency amplitude modulator l1 45l for amplitude-modulating thecarrier wave generated in local oscillatorl I8 with the video-frequencycomponents generated in unit III and arnplied in unit I6, Whilemaintaining the frequency constant during all of the trace periods.'I'here is also included a. single sideband filter I9, a frequencychanger 20, a heterodyne frequency filter 2|, a power amplifier 22, andan antenna system 23, 24, as shown, the frequency changer 20 comprisingmeans for eiecting a change of frequency of and frequency-modulating,the carrier wave generated in master oscillator I8 in accordance withsynchronizing-signal components, while maintaining its amplitudeconstant during al1 of the retrace periods.

Neglecting for the moment the stages I9, 20, and ZI and thesynchronizing-signal-generating apparatus provided in accordance withthe present invention, the system just described includes the apparatusof a television transmitting system of conventional design, those partsofthe system illustrated schematically being of any wellknown suitableconstruction, so that a detailed description of the `system and itsoperation is un. necessary herein. Briefly, however, the image of thescene to be transmitted is focused upon the target of the tube II, inwhich a cathode ray or beam is developed, accelerated, and also focusedupon the target. Scanning or deflection currents developed by thegenerators I2 and I3 are applied to the scanning elements or windings Iland IIb and serve to deflect the ray to scan successive series or fieldsof parallel lines on the target. Pedestal impulses developed by thegenerator Il are applied to the control electrode of the tube II to`suppress or block out the beam during certain portions, particularlyretrace portions, of the scanning cycles and are applied to themodulation-frequency amplifier I to suppress undesirable impulsesdeveloped in the system and to aid in obtaining the required wave form of the video-modulation signal.

The photosensitive elements of the target being electri-ally affected toan extent depending upon the varying values of light and shade atcorresponding incremental areas of the image focused thereon, as thecathode ray scans the target, a voltage of correspondingly varyingamplitude is developed in the output circuit of the signal-generatingtube and applied tothe amplifier I6. Suitable timing-or synchronizingimpulses are applied from the generator I5. to the generators I2, I3,and I4 to maintain these generators in synchronism with either themaster frequency, in the case of direct camera shots, or the motionpicture camera, in the case where such pictures are being transmitted.-The video-signal com. c

`in accordance with video-signal components during trace periods, whilemaintaining its frequency constant during all of the trace periods, andmeans for frequency-modulating the carrier wave in accordance withsynchronizing-signal com-- ponents during retrace periods, whilemaintaining its amplitude constant during all of the retrace periods, aswill be presently explained. The

`and' field-synchronizing impulses, respectively.

In a preferred arrangement, for example, the line-scanning andfield-scanning frequencies may be 13,230 and 60 cycles per second,respectively, and the frequencies developed by the generators 25 and 25may be 1.00548 megacycles and 0.240 megacycle, respectively, that is,the '16th and 4000th harmonics of the line-scanning and fleldscanningfrequencies, respectively, as will be hereinafter further explained.

While the generators I2 and I3 develop currents of the saw-tooth waveforms indicated at the left of these generators and at their respectivefrequencies, they also, in accordance with well-known practice, generaterectangular-impulse waves of the form shown at the right of thesegenerators and of the same frequencies. These impulse waves are timed tofall within, and have durations somewhat less than, the line-retrace andfield-retrace periods, respectively, although they are preferably causedto have durations as nearly equal to those of the line-retrace andfield-retrace periods as possible. Output circuits of the generators I2and 25 are connected to a mixing amplifier 21, while output circuits of.the generators I3 and 26 are connected to a mixing amplifier 28, theoutput circuits of the generators I2 and I3 supplying the impulses ofrectangular wave form. The ampliners 21-and 28 may be of conventionaldesign and are ncrresultantmo'dulated-carrier wave is amplified in thepower amplierv 22V and is thereupon im pressed upon the antenna system23, 24 for radiation.

`Corning now to that partv of the system embodying the presentinvention, it, will first be @noted that the single sideband filter I9may be of any suitable well-known Vdesgri. preferably having acharacteristic such as is shown vby the curve -of Fig. 8,.whereinrelative gain is plotted against frequency, `as indicated. that is, acharacteristic c such that the band-pass selector or filter I9translates the carrier signal' and that'one of its modulation`Asidebands on the side of the frequency to which the frequency of thecarrier wave is shifted to translate synchronizing signals, ashereinafter more fully described. Specifically the selector is designedto have a response characteristic with a sloping side and a meanfrequency so related to the carrier frequency developed by the modulatorl1 that this frequency is located on the sloping side thereof, asindicated at X in Fig. 3, so that, although the sideband frequenciescorresponding to the lower modulation adjacent the carrier frequenciesare passed with relatively less gain, a portion of c ing thesefrequencies is passed by the selector so that the over-all gain issubstantially the same for these lower modulation frequencies as for thehigher modulation frequencies. The heterodyne frequency filter 2l is ofany suitable conventional type designed to pass'either the difference orsun both sidebands represent- For the purpose of frequencymodulatingthe' mally biased beyond cutoff, so that the rectangular impulses of thewaves supplied from generators I2 and I3 carry these amplifiers abovecutoff, rendering them operative for the durations of 1 Therefore, thereaptheir respective impulses. pear in the output circuits of theamplifiers 21 and Y2'8 trains of sinusoidal voltage waves of Ylinethepredetermined vportions* thereof corresponding to the durations of thepulses developed by the generators I 2 and I3, respectively.

carrier wave' impresed upon the frequency changer 2 0 from the filterI!l during the retrace periods in accordance with thesynchronizingsignal components, there is provided thefrequency-modulating or frequency-shifting apparatus indicated generallyat 29. This apparatus includes an oscillator indicated generally at 30and a frequency-adjusting network indicated generally at 3| Preferablythe oscillator is of the push-pull typecomprising vacuum tubes 32 and33, having their input circuits connected in push-pull relation by wayof an inductance 34,

a leak resistor 35 and grid condenser 35a being connected in parallelbetween a midtapon the inductance 34 and the cathodes of the tubes.'I'he anode circuits of the tubes 32 and 33 are also connected inpush-pull relation by way of an inductance 38, coupled to the inductance34 as indicated by bracket' M, a mld-tap on the inductance 36 beingconnected to the cathodes of the tubes by way ofl anode voltage supplybattery 31. The inductance., 36 is normally sharply tuned to a frequencyspaced from the carrier frequency developed by the'modulator |1, bymeans of a condenser 38 or other suitable 'circuit arrangement. Aninductance 39 is coupled to` the inductance `Sli and connected to thefrequency changer 2|) for the purpose of 4shifting the carrier frequencydelivered'fromthe filter I9 in accordance withvfrequcncies developed bythe oscillator 30.

The frequency-adjusting network 3| prefer ably comprises a'pair ofvacuum tubes 40 and 4| having their control grids connected by way ofresistors 42 and 43 to the output circuits of the amplifiers 21 and 28and by way of by-pass condenser 44 which is effective to by-passoscillator-frequency currents to ground. The control grids of rthe tubes40 and 4| are also connected by way of coupling condensers 45,V 46 totheir respective anodes which, in turn, are con- 4nected to'theterminals of an inductance 41.

The inductance 41 is connected in push-pull relation in the anodecircuits of `the tubes, a. mid-tap thereof being connected to the tubecathodes by way of a suitable anode voltage supply source, indicated bythe battery 48. The inductance 41 is inductively coupled to theinductance 36 of the oscillator frequency-determining circuit.

In the operation of the parts of the transmitter embodying thev presentinvention, referring first to thefrequency-adjusting network 3|, whichit will be assumed is excited from oscillator 30, it will be seen'that,since the impedances of the condensers 45 and 46 are high compared withthose of resistors 42 and 43, the voltages across the resistors lead thevoltage across the inductance 41 by a large angle and that the spacecurrents of the tubes, being in phase with the tube input voltages, alsolead the voltage across theinductance 41 in corresponding degree. Hence,the system simulates an impedance having capacitive reactance andresistance components, the values of which vary in accordance with thegrid-bias voltage applied to the tubes. Adjustment of the grid-biasvoltage on the tubes 40 and 4|, therefore, varies the effectivereactance oi' the circuit 3| and, hence, the natural frequency of theoscillation circuit 36, 38 to which it is coupled.

Normally the tubes 40 and 4| are biased beyond cutoff' and remain sobiased during the video-signal or trace periods, being renderedoperative only Vduring synchronizing or retrace periods when impulsesfrom one or both of the generators |2 and I3 are applied thereto. Sincethe tubes 40 and 4| are cut 0E during the videosignal periods, theoscillation circuit 36, 38 has its own natural frequency during theseperiods, while its frequency is shifted in the desired manner during theoccurrences of the .synchronizing impulses. During the latter periodsthe impedance reflectedinto the oscillation circuit 38, 38 bythefrequency-adjusting network 3| harmonic and field-harmonic voltagesapplied to the grids of the tubes 4|) and 4| from theA generators and 26as controlled in ampliflers 21 and` 28 by the impulses from generators|2 and I3, respectively, so that the frequency of the oscillationcircuit is intermittently varied is varied in accordance with `theline-v cyclically in a manner that will presently be further explained.

The oscillator 30 being-coupled as above described to the frequencychanger 20,' its frequency is mixed with the carrier frequency of thevideo-modulated signal delivered from the filter I9 and the sum anddifference heterodyne frequencies are developed iny the output circuitof the modulator in the well-known manner. Either the sum frequencies orthe difference frequencies are selected by means -of the filter 2| anddelivered to the powerf'ampliiier 22 to be broadcast. Similarly, thefrequency of the selected heterodyne carrier output of frequency changer20 is cyclically varied or shifted in correspondence with the frequencyvariations of oscillator 30, as described above.

In Fig. 3, there is illustrated half'of the envelope of the resultantmodulated-carrier wave developed by vthe transmitting system. Thevideo-frequency signal component is represented at the portions of thewave indicated at V and is developed during line-trace periods, the por?tions representing line-retrace and field-retrace periods, during whichthe frequency of the carrier is shifted or varied, being indicated at Land F, respectively. In Figs. 4 and 5 there are shown exploded curvesillustrating the cyclic frequency variations of the carrier wave duringthe line-retrace and held-retrace periods L and F, respectively. Inthese figures, the abscissae represent time and the ordinates frequencyshift or deviation of the signal carrier.

Thus, the carrier wave developed in the output circuit of the modulater|1 is amplitudemodulated bythe video-signal components only during thetrace scanning periods, and during these periods the frequency developedby the generator 30 and applied to the frequency changer 20 is constantso that the carrier frequency as developed in the output circuit of thefrequency changer 20 is not varied. During a portion of the line-retraceperiods the impulses from the generator 2 unblock the amplifier 21 andpermit the line-harmonic voltages developed by the generator 25 to bepassed by the amplifier 21 and impressed on the frequencyadjustingnetwork 3|, thereby to effect variations in the frequency developed bythe generator 30 and, hence, in that of the carrier frequency developedin the frequency changer 26, as indicated by the curve of Fig. 4.-During one or more' portions of the field-retrace periods, on the otherhand, the impulses from the generator I3 unblock the amplifier 28 andpermit the fieldharmonic voltages developed by the generator 26 to bepassed by this amplifier and impressed on the network 3|, thereby toeffect variations in the frequency developed by the generator 30 indifferent predetermined manners for the lineand field-synchronizingsignals, specifically in different intermittent cyclic manners and,hence, in that of the carrier-frequency output circuit of the frequencychanger 28, as indicated by the curve of Fig. `5. Thus, the carrier wavedeveloped in the output circuit of modulater |1 is frequency-modulatedin frequency changer 2l by the synchronizing-signal components duringall of the retrace periods. The amplitude of the carrier-frequencyoutput circuit of frequency changer 20 is maintained constant during allof the retrace periods and the carrier signal comprising bothamplitude-modulation and frequency fmodulation components is directlyradiated after translation in units 2| and- 22.

the ,synchronizing-signal' components in accord- Since the outputfrequencies of the generators 25 and 26 are harmonics of theline-scanning and eld-scanning frequencies, the successive pulse groupsare all of the same phase and wave form, and vare not subjected toprogressive changes in wave form from'one group to the next, as would bethe case if a nonharmonlc cyclic variation were employed. The cycles bfvariation which correspond to the line-synchronizing impulse are thus ofone predetermined frequency: that is, the carrier frequency is varied.in one manner and for a first predetermined duration. A linesynchronizing period immediately precedes each field-synchronizingperiod, as shown in Figs. 3 and 5, so that line synchronization is notinterrupted during eld-retrace periods.

Referring now to Fig. 2, the system there illustrated comprises atelevision receiver of the superheterodyne type for receiving andreproducing a program transmitted by a carrier wave of the typedeveloped by the transmitter -de scribed above. This receiver includesmeans for selectively receiving the carrier wave and specificallyincludes an antenna system 50, 5| to which there are connected 'incascade, in the order named, a radio-frequency amplifier and frequencychanger 52, an intermediate-frequency amplifier 53, a detector 54comprising means for detecting the amplitude modulation to derive thevideo-signal components, va video-frequency amplifier 55, and acathode-ray signal-reproducing tube 56 comprising means for utilizingthe detected video-signal components to reproduce the transmittedprogram. Preferably, as explained below, the stages 52 and 53 aredesigned for single sideband reception. A linefrequency scanninggenerator 51 and field-frequency scanning generator 58 are also coupledto the output of the amplifier 53 by way ofsynchronizing-signal-deriving apparatus 59 embodying the presentinvention and .hereinafter described in more detail. The generators 51and `58 are coupled to the scanning elements of the mediate-frequencysignals being, in turn, selec tively amplified in theintermediate-frequency amplifier 53' and delivered to the detector 54.

The video-modulation components of the signal y are developed by thedetector 54 and are supplied to the video-frequency amplifier 55,wherein they are amplified and. from which they are supplied in theusual manner to' a brilliancy .control electrode of the cathode-ray tube56. The intensity of the" electron beam of the tube '56 1s thus modifiedor controlled in accordancewith the video-frequency voltages` impressedupon the control electrode of the tube in the usual manner.

The intermediate-frequency signal is also supplied from the amplifier 53to the apparatus 59 comprising means responsive to the frequencymodulation of the received carrier for detecting ance with the presentinvention, the line-'synchronizing and field-synchronizing componentsbeing effectively separated from the video-freque y signals and fromeach other and applied to e control circuits of the generators 51 and 58as will be hereinafter further explained. Saw-tooth current/or voltagescanningA waves are\ generated 'in the line-scanning and fieldscanninggenerators 51 and 58 and applied to e scanning elements of thecathode-'ray tbe 56 to produce electric scannin fields, thereby todeflect the intensity modula cathode ray vertically vand horizontally soas to trace successive fields of parallel lines on the target of thetube to reconstruct'the transmitted image.

For the purpose of more effectively receiving and reproducing a signalof the single sideband type transmitted, fofI example, from atransmitter such as described in connection with Fig. 1, the frequencychanger 52 is arranged to n develop such an intermediate-frequencysignal that the intermediate-frequency carrier is normally located onone of the sloping sides of the band-pass characteristic of the selector53, which is similar to that of the filter I9 of the system of Fig. 1illustrated in Fig. 8. Referring now more particularly to thesynchronizing-signal-deriving apparatus 59, there is here provided anamplifier '60 having its input circuit connected tothe output circuit ofthe intermediate-frequency amplier 53 and its output circuit connectedin turn to a broad single sideband selector 6|. The selector 6| alsopreferably has a band-pass characteristic similar to that of the filterI9 of Fig. 1, that is, so designed that theintermediate-frequencycarrier is located on one of its sloping sides. The amplifier 60 andselector 6| serve to provide a signal of sufdcient amplitude to ensureproper operation of the succeeding parts of the apparatus 59. Due to thecharacteristics of the amplifier 53 and selector v6|, the shift in theintermediate-frequency carrier from the sloping side of the band-passcharacteristic to the uniform higher response portion thereof during theretrace periods effectively increases the amplitude of the carrieroutput of selector 6| so that the form of the wave developed in theoutput circuit ofthe selector 6| is as'shown in Fig. 6.

Connected in cascade to the output circuit of the selector 6|, in theorder named, are a vacuu'm-tube limiter 52, a band-pass selector 63, avacuum-tube amplifier 64,.a modulation .converter or selector 65, adouble-diode rectifier circuit,66, and parallel-connected band-passfilters 61 and 63. The limiter 62 preferably comprises a f resistor6212, as-shown, and has an operating .characteristic as illustratedv inFig. 9, the points X-X indicating generally the range of operation ofthe tube beyond both its upper and lower cutoff limits for any usefulreceived signal. Y Due to the action of the limiter, only a smallportion of the wave received from selector 6|, such as that indicated ats in Fig. 6, is'passed by the limiter 62. The condenser 62a and leakresistor 62h provide a self-biasing or stabilizing action forthelimiterso that the interval s is alwaysimmediately below the peaks ofthe signal and independent of the signal amplitude. The half-envelope ofthe voltage developed in the output circuit of the limiter, therefore,is as illus- `trated by the curve ofFig. 7. Y

.The selector 63 may comprise primary and secondary windings u anditfeach broadly 'output Pulau oflimiter l2. The tube u, to-

gethen'with selector il, serves to couplethe limiter l! to themodulation converter or` selector 6i and to prevent back couplingbetween the circuits. Asuitablebiasingbatteryaispreferablypmvldedinthegridcircuitofthetube .5.4. as shown.'.lheselector' may be 'constructed similarly to the selector l2 andcomprise transformer `windings 12 and 14, eachtunedhyaccndenserllshuntedbyaresistor 16. VThis selector, however, ispreferably so tuned as tohave a transmission characteristic such las isillustrated by .the curve of Fig. 10, wherein relative gain' in volts isplotted against frequency, in mealycb, relative to theintermediate-can'ier frequency developed by the oscillater-modulatorzl2. Selector Si is thus a bandpassselectorfortranslatingthecarersignalhaving a response characteristic with a sloping -side and of ameaufrequency so related to the normal frequency of the carrier that thelatter is located on the sloping side. Thus,l thisselector comprisesmeans responsive to periodic frequency variations of the receivedcarrier wave and serves the purpose of converting the frequency shiftsor modulation into amplitude variations; that is, the amplitude of itssignal output varies in accordance with its input v frequency shifm orvariations.

Therectifiermaycompriseapairofdiode rectiiim I'l and 1l connectedacrossthe secondary circuit of the selector Il for full-wave reciicaticn andprovided with a load resistor 1l. The volh'ge acrossload resistor 18 isapplied `negatively to the input circuits of the filters 61 and Il.The-filters Il and Il are preferably timed so that they are moetresponsive at frequencies corresponding to the cyclic carrierfrequencyvariations occurring during the line retrace and field-retrace periods,respectively,

- that is, to frequenci of the oscillations generated by circuiis 2i and26, respectively, at the transmitter of Pig. 1. In the present case, forexample,thefilte1si1andlmaybetunedto 1.0 and 0.24 megacycles,respectively'. In order that these filters will have a reasonably rapidresponse, they are preferably designed with relatively wide hand-passcharacteristics, for example, of the order of :50% of their respectivemean resonant frequencies. 'Ihe output circuits of the filters l1 and Ilmay be connected to the line-scanning and field-scanning generators 51and il, respectively, for delivering synchronizing impulses thereto.

, In the operation of the apparatus 59, 4the inimmediate-frequencycarrier and its single side- 'band of modulation frequencies aredelivered increase Yin the carrier amplitude output of selector ilduring each line-scanning and fieldscanning period.

The tube 62 serves, as described above, to limit the signal,therebyeiiectively to separate the synchronizing-signal componentsthereof from the video-signal components and to provide a signal in itsoutput circuit, the half-envelope of which is illustrated in Fig. 7.This signal is delivered by way of the selector il and amplifier 64to'the modulation converter or selector l5 and therein eectivelyconverted into a signal, the amplitude of which variesor is modulated inaccordance with .shifts or modulation of the frequency of theintermediate-frequency carrier. This signal is thereupon impressed uponthe diode rectifier 6I. The rctier functions to develop across its loadresistor 19 a periodicimpulse signal comprising two components eachincluding recurring impulses. The frequency and duration ,of vtheimpulses of one component correspond to the line-scanning impulsesdevelopedfby the transmitter generator I2, while the frequency andduration of the impulses of the other component correspond to thefield-scanning impulses developed by transmitter gener-- determined bythe transmitter generators 25 and 26, respectively. The lters 61 arid 88are designed to be most responsive to such line-har- .monic andheld-harmonic frequencies, respectively, and thus comprise meansresponsive to the variations ,of the frequency of the carrier wave in afirst predetermined manner for deriving line-synchronizing componentsand means responsive to variations of the frequency of the carrier wavein a different predetermined manner for deriving held-synchronizingcomponents. It will be noted that the envelopes of the waves passed bythe filters I'Land 6I constitute periodic waves comprising impulsesoccurring at the linescanning and held-scanning frequencies,respectively, these impulses being impressed upon the generators 5l and58, respectively, and serving to synchronize their operation inaccordance with the corresponding generators l2 and I3 at thetransmitter.

In the event that it is desired not to utilize the cyclic or harmonicvariation feature of the invention, the generators 25 and 26 of thetransmitter may be omitted so that the generators i2 and I3 and theapparatus 29 simply eifect a single shift of the signal-carrierfrequency into a portion of the frequency spectrum occupied by asideband of the amplitude-modulated signal during eachline-synchronizing and field-synchronizing impulse, which shift has aduration equal tothat of its respective impulse. In this case, thereceiver lters 6l and B8 may be omitted and any suitable signal durationresponsive device may be substituted therefor. Such a device functionsin a conventional manner to separate the line-synchronizing andfield-synchronizing impulses in response to their relative durations andto deliver the derived linevsynchronizing and field-synchronizingimpulses to the generators 51 and'58, respectively. For this purpose,idlerefore, the input and output terminals of the filters "and 68 may bedisconnected at the points indicated at A, B, and C, and a suitableduration responsive separator 80, such as indicated in Fig. 2a, may haveits corresponding terminals, also indicated at A, B, and C, connected tothese points. The device may be of any suitable well-known design, suchas that shown in applicantfs copending application, Serial No. 177,679,filed December 2, 1937, for Television scanning systems.v

Moreover, if desired, the frequencies to which the carrier is shiftedduring the line-scanning 'and field-scanning pulses may be of differentpredetermined values, in which case Ithe devices Ulf-8l, inclusive, maybe replaced by two selectors 8| and 82, as shown in Fig. 2b, sharplytuned to these respective frequencies and having individual rectifiers83 and 84,' suitably connected to the scanning generators 51 and 58,respectively.

' Similarly to Fig. 2a, the several points of connection for thecircuits of Fig. l2b in the system of Fig. 2 are indicated at B, C, andD. With this `or similar arrangements, if desired, a section of themodulation envelope below that represented at s may be selected by thelimiter 62. For this purpose it is .necessary only to adjust the valueof the bias to an appropriate more negative value vandto omit theself-biasing elements 62a and.

B2b. r

It is to be noted that, in both arrangements described above, theadvantage of an increase in synchronizing-signal amplitude, without anycorresponding increase in power output at the transmitter is obtained bymeans of single sideband transmission and the special band-pass filtercharacteristic which has been described, employed at either or both thetransmitter and receiver. It will, however, be appreciated that thatsingle sideband feature may, if desired, be omittetdfk from a systemembodying the other y While there have been described what are atpresent considered to be the preferred embodiments of this invention, itwill be obvious to those skilled in the art that various changes andmodications may be made therein without departing from the invention,and it is, therefore, aimed in the lappended claims to cover all suchchanges and modications as fall within the, true spirit and scope of theinvention.

1. A television broadcast system comprising a station for developing andtransmitting a modulated-carrieriwave including means for developingvideo-signal components during `trace periods and synchronizing-signalcomponents during retransmitted wave including means responsive toamplitude modulation of the received carrier for detecting and utilizingsaid signal components -of said one type, and means responsive tofrequency'modulation of the received carrier for detecting and utilizingsaid components of said other type.

2. A television broadcast system comprising a station for developing andradiating va high'- frequency modulated-carrier vwave including meansfor developing video-signal components during trace periods andsynchronizing-signal components during retrace periods, means foramplitude-modulating said carrier wave in accordance with saidvideo-signal components, means for frequency-modulating said carrierwave in accordance with said synchronizingsignal components, means foi'directly radiating said amplitudeand frequency-modulated carrier wave,and a station for receiving and reproducing said transmitted waveincluding means responsive to amplitude modulation of the received lcarrier for detecting and utilizing saidvideosignal components, andmeans responsive to frequency modulation of the received carrier fordetecting Aand utilizing said synchronizing-signal components.

3. A television broadcast system comprising a station for developing andtransmitting a modulated-carrier wave representing successive trace andretrace periods including means for developing a carrier sinvavenormally of a predetermined frequency, means for developing video-signalcomponents and synchronizing-signal ponents, means foramplitude-modulating said carrier wave during trace periods inaccordance with said video-signal components, means for shifting thefrequency of saidl carrier wave during retrace periods into a portion ofthe frequency spectrum occupied by a sideband of saidamplitude-modulated signal and in accordance with saidsynchronizing-signal components, and a stationfor receiving andreproducing said transmitted wave includingmeans responsive to amplitudemodulation of the received carrier for' detecting and utilizing saidvideo-signal components and `means 'responsive' to frequency variationsof the received carrier for developing and utilizing saidsynchronizing-signal components.

4. A television transmitting system comprising means for developing acarrier wave, means'for developing video-signal components during traceperiods, means for developing synchronizingsignal components duringretrace periods, means for amplitude-modulating said carrier wave inaccordance `with signal components of one of said types andformaintaining its frequency constant during all of said periodscorresponding to said one of said types, means for frequency-modulatingsaid carrier wave in accordance with signal components of the other ofsaid types and for maintaining its amplitude constant during all of saidperiods of said other of said types, 'and means for transmitting saidmodulated-carrier-wavel 5. A television transmitting system comprisingmeans for developing a carrier wave, means for developing-video-signalcomponents, means for developing synchronizing-signal components, meansfor amplitude-modulating saidl carrier wave during trace periods inaccordance with said video-signal components, means forfrequency-modulating said carrier wave during rea radiating saidmodulated-carrierv wave. f

6. A television transmitting system comprising means for developing 'acarrier wave normally of a predetermined frequency, means for developingvideo-signal components, means for develop- COming synchronizing-signalcomponents, means for amplitude-modulating said carrier wave\during'tace periods in accordance with said videosignal-components. means forshifting the frequency of said carrier wave during retrace periodsinto`a portion of the frequency spectrum occupied 4by a sideband of saidamplitude-modulation compon`ents and in accordance with saidsynchronizing-signal components, and means for transmitting saidmodulated and frequency-varied carrier wave.

7. A television transmitting system comprising means for developing acarrier wave normally of a `predetermined frequency, means fordeveloping video-signal components, means for developing line-frequencysynchronizing impulses. means for developing field-frequencysynchronizing impulses, means for amplitude-modulating said carrier waveduring4 trace periods in accordance with said video-signal components,means for varying the frequency of said carrier wave for a firstpredetermined duration during at least a portion of saidline-synchronizing impulses, means for varying the frequency of saidcarrier wave fora different predetermined duration during at least aportion of said field-synchronizing impulses, and means for directlyradiating said modulated, frequency-varied carrier wave.

v8. A television transmitting system comprising meansfor developing acarrier wave normally of a predetermined frequency, means for developingvideo-signal components, means for developing line-frequencysynchronizing impulses, means for developing field-frequencysynchronzing impulses, means for anplitude-modulating said carrier waveduring trace periods in accordance with said video-signal components andfor maintaining its frequency constant during all of said trace periods,means yfor varying the frequency of said carrier in a iirstpredetermined manner during line-retrace periods, in accordance withsaid line-synchronizing impulses and for maintaining its amplitudeconstant during allof said line-retrace periods, means for varying thefrequency of said carrierin a different predetermined manner duringfield-retrace periods in accordance with said field-synchronizingimpulses and Afor maintaining its amplitude constant during all of saidfield-retrace periods, and means for transmitting said modulated,frequency-varied carrier Wave.`

9. A television transmitting system comprising means for developing a`carrier wave normally of a predetermined frequency, means fordeveloping` video-signal components, means for developing line-frequencyand field-frequency waves having trace and retrace periods, means forarn plitude-modulating said carrier wave during trace periods inaccordance with said video-signal components, means for varying thefrequency of said carrier in a first predetermined manner and for afirst predetermined duration during 1ineretrace periods, means forvarying the frequency of said carrier in a diiferent predetermined man.ner and for a diiferent predetermined duration during field-retraceperiods, and means for transmitting said modulated, frequency-variedcarrier wave.

10. A television transmitting system comprising means for developing acarrier wave normally of a predetermined frequency, means for developingvideo-signal components, means for developing line-frequency andlfield-frequency scanning waves having trace and retrace periods, meansfor amplitude-modulating said carrier assises wave during successivetrace-scanning periods in accordance with said video-signal components,means for varying the frequency of said carrier in one or moresuccessive cycles of predetermined frequency during successiveline-retrace-scanning periods, means for varying the frequency of saidcarrier wave in one or more successive cycles of a differentpredeterminedJ frequency during successive field-retrace-scann'ingperiods, and means for transmitting said modulated, frequency-variedcarrier wave.

11. A television transmittiig system comprising means for developing acarrier wave normally of a predetermined frequency, means for developingvideo-signal components, means for developing line-frequency andfield-frequency scanning waves having trace and retrace periods, meansfor amplitude-modulating said carrier wave in accordance withvideo-signal components during trace periods, means for shifting thefrequency of said carrier wave with respect to said predeterminedfrequency and in accordance with synchronizing-signal components duringretrace periods, a band-pass selector for translating said carrier andthat one of its modulation sidebands on the side of said predeterminedfrequency to which said carrier frequency is shifted, said selectorhaving a response characteristic with a sloping side and having a meanfrequency so related to said predetermined carrier frequency that thelatter is located on said sloping side, and means f or transmitting thefrequencies translated by said selector.

12. A television receiving system for receiving and reproducing aprogram transmitted by a car' rier wave having amplitude modulation andfrequency modulation, one of said types of modulation representingvideo-signal components during trace periods and the other of said typesof modulation representing synchronizing-signal components duringretrace periods and said carrier wave being of constant frequency duringall of said periods corresponding to said amplitude modulation and ofconstant amplitude during all of said periods corresponding to saidfrequency modulation, comprising means for selectively receiving saidcarrier wave, means for detecting signal modulation of said one of saidtypes to derive said video-signal components, means for detecting signalmodulation of said other of said types to derive saidsynchronizing-signal components, and means for utilizing said derivedcomponents to reproduce theA transmitted4 program.

13. A television receiving system for receiving and reproducing aprogram transmitted by a di rectly radiated carrier wave havingamplitude modulationrepresenting video-signal compolation representingsynchronizing-signal components during retrace periods, comprising meansfor selectively receiving said signal, means for amplitude-detectingsaid carrier to derive said video-signal components, means forfrequencydetecting said carrier to derive said synchronizing-signalcomponents, and'means for utilizing saidr derived components forreproducing the transmitted program.

14. A television receiving system for receiving and reproducing aprogram transmitted by a carrier wave normally of a predeterminedfrequency and amplitude-modulated in accordance with video-signalcomponenisduring Y, trace periods but having its frequency periodicallyshifted into a portion of the frequency spectrum oclated signal and inaccordance with synchromining-signal components during retrace periods,comprising means for selectively receiving said carrier wave, meansresponsive to periodic frequency variations of said carrier wave forderiving said synchronizing-signal components, detectingamplitude-modulation means for deriving said video-signal components,and means for utilizing said derived components for reproducing thetransmitted program.

15. A television receiving system for receiving and reproducing aprogram transmitted by a carrier wave normally of a predeterminedfrequency but having its frequency,1 shifted for a rst predeterminedduration during line-retrace periods while its amplitude is maintainedconstant during all of the line-retrace periods and shifted for adifferent predetermined duration during eldretrace periods while itsamplitude is maintained constant during all of the field-retrace periodsand amplitude-modulated during trace periods in accordance withvideo-signal components while its frequency ismaintained constant duringall of said trace periods, comprising means for selectively receivingsaid carrier wave, amplitude-modulation detecting means for derivingsaid video-signal components, means responsive to frequency variationsof said carrier Wave of said first predetermined duration for derivingsaid line-synchronizing components, means responsive to frequencyvariations of said carrier wave of said different predetermined durationfor deriving said field-synchronizing components, and means forutilizing said derived components for reproducing the transmittedprogram.

16. A television receiving system for receiving and reproducing aprogram transmitted by a carrier wave normally of a predeterminedfrequency and amplitude-modulated during trace periods in accordancewith video-signal com-ponents but having its frequency shifted in afirst predetermined manner during line-retrace periods in accordancewith line-synchronizing components and having its frequency shifted in asecond predetermined manner during eldretrace periods in accordance withsaid fieldsynchronizing components into a portion of the frequencyspectrum occupied by a sideband of said amplitude-modulated signal,comprising means for selectively receiving said carrier wave,amplitude-modulation detecting means for de-l riving said video-signalcomponents, means responsive to variations in the frequency of saidcarrier wave in said first predetermined manner for deriving saidline-synchronizing components, means responsive to variations in thefrequency of said carrier wave in said different predetermined mannerfor deriving said held-synchronizing components, and means for utilizingsaid derived components for reproducing the transmitted program.

17. A television receiving system for receiving and reproducing aprogram transmitted by a carrier wave normally of a predeterminedfrequency but having its frequency shifted in a iirst predeterminedmanner for a first predeterminedA duration during line-retrace periodsin accordance with line-frequency synchronizing components while itsamplitude is maintained constant during all of the line-retrace periodsand having field-frequency? synchronizing components while 'itsamplitude is maintained constant during all of the held-retrace periods,said 'carrier wave being amplitude-modulated during trace periods inaccordance with videosignal components while its frequency is maintainedconstant during all of said 4trace periods, comprising means forselectively receiving said carrier wave, amplitude-modulation detectingmeans for deriving said video-signal components, means responsive tovariations in the lfrequency of said carrier Wave in said rstpredetermined manner and of said first predetermined duration forderiving` said line-synchronizing components, means responsive tovariations in the frequency of said 4 carrier wave in said diierentpredetermined lation frequencies manner and of said differentpredetermined duration for deriving said field-synchronizing components,and means for utilizing said derived components for reproducing thetransmitted program.

18. A television receiving system for receiving and reproducing aprogram transmitted by a carrier wave and a sideband ofamplitude-modurepresenting video-signal components during successivetrace periods, said carrier being normally of a predetermined frequencybut shifted with'respect to said predetermined frequency duringsuccessive retrace periods in accordance with synchronizing-signalcomponents, comprising means for selectively receiving said carrierwave, amplitude-modulation detecting means for deriving saidvideo-signal components, a band-pass selector for translating saidcarrier having a response characteristic with a sloping side and of amean frequency so related to said predetermined frequency that thelatter is located on said sloping side, means responsive to the signaloutput of said selector for deriving said synchronizing-signalcomponents,

and means for utilizing said derived components 'manner for a differentpredetermined duration during field-retrace periods in accordance withto reproduce the transmitted program.

19. A television receiving system for receiving and reproducing aprogram transmitted by a carrier normally of a predetermined frequency,but having its frequency varied Athrough one or more cycles of onefrequency during line-retrace periods and varied through one or moredifferent cycles of a diiferent frequency during fieldretrace periodsand amplitude-modulated during trace periods in accordance withvideo-signal components, comprising means for selectively receiving saidcarrier wave, amplitude-modulation detecting means for deriving saidvideosignal components from said received carrier wave,frequency-modulation detecting means for deriving from said receivedcarrier wave said cyclic frequency modulation, resonant circuit meanstuned to the respective frequencies of said one of said different cyclicvariations for deriving synchronizing impulses, and means for utilizingsaid derived video-.signal components and said synchronizing impulsesfor reproducing the transmitted program.

20. The method of transmitteing and receiving a television program whichcomprises, developing video-signal components during trace periods and'synchronizing-signal components during retrace periods,amplitude-modulating said carrier wave in accordance with said signalcomponents of one of said types while inaintaining its frequencyconstant during all of said periods corresponding to said one of saidtypes, frequency-modulating said carrier wave in accordance with saidsignal components of the other of said types while maintaining itsamplitude constant during all of said periods corresponding to saidotherofsaid types, transmitting said modulated-carrier wave, selectivelyreceiving said transmitted carrier wave, detecting said amplitudemodulation of the received carrier to derive said signal components ofsaid one type, detecting said frequency modulation of the receivedcarrier to derive said signal components of said other type, andutilizing said derived components to reproduce the program.

21. The method'oftransmitting and receiving a television program,comprising developing video-signal components during trace periods andsynchronizing-signal components 'during retrace periods,amplitude-modulating said carrier wave in accordance with saidvideo-signal components, frequency-modulating said carrier wave inaccordance with said synchronizingsignal components, directly radiatingsaid modulated-carrier wave, selectively receiving said transmittedwave, detecting said amplitude modulation of the received carrier toderive said video-signal components, detecting said frequency modulationof the received carrier to derive said synchronizing-signal components,and utilizing said derived components to reproduce said program. A

22. The method of transmitting and receiving a television program,comprising developing a carrier wave normally of a predeterminedfrequency and representing successive trace and retrace periods,developing video-signal components and synchronizing-signal components,amplitude-modulating said carrier wave during said trace periods inaccordance with said video-signal components, shifting the frequency ofsaid carrier wave during said retrace periods in accordance with saidsynchronizing-signal components into a portion of the frequency spectrumoccupied by a sideband of said amplitude-modulated signal, transmitting`said modulated, frequency-varied carrier wave, selectively receivingsaid transmitted wave, detecting said amplitude modulation of thereceived carrier to derive said video-signal components, detecting saidfrequency variations of the received carrier to derive saidsynchronizing-signal components, and utilizing said derived componentsto reproduce `said program.

23. The method of transmitting a television program, comprisingdeveloping a carrier wave, developing video-signal components duringtrace periods, developing synchronizing-signal components during retraceperiods, amplitude-modulating said carrier wave in accordance withsignal components of one of said types while maintaining its frequencyconstant during all of said periods corresponding to said one oi' saidtypes, frequency-modulating said carrier wave in accordance with signalcomponents of the other of said types while maintaining its amplitudeconstant during all of said periods corresponding to said other of saidtypes, and transmitting said modulated-carrier wave.

24. The method of transmitting a television program, comprisingdeveloping a carrier wave. developing video-signal components,developing synchronizing-signal components, amplitudemodulating saidcarrier wave in accordance with said video-signal components duringtrace-scanning periods, frequency-modulating said carrier wave duringretrace-scanning periods in accordance with said synchronizing-signalcomponents,

vand directly radiating said modulated-carrier ,wave. 25. The method ofa television developing video-signal components;

program, comprising developing a carrier wave,

line-frequency and nem-frequency scanning waves having trace and retraceperiods, amplitude-modulating said carrier wave in accordance with saidvideo-signal components during one .or more successive cycles -of onepredetermined frequency during lineretrace scanning periods, varying thefrequency of said carrier wave in one or more successive cycles of adifferent predetermined frequency during successive field-retracescanning periods, and transmitting said amplitude-modulated and yfrequency-varied carrier wave.

' said signal, detecting amplitude modulation of the received carrier toderive said wideo-frequency components, detecting frequency modulationof lthe received'carrier to derive sai synchronizing-signal components,and utilizing said derived components for reproducing the transmittedprogram.

27. The method of receiving and reproducing a television programtransmitted by a carrier wave normally of a predetermined frequency andamplitude-modulated in accordance with videosignal components duringtrace periods but having its frequency shifted in accordance withsynchronizing-signal components during retrace periods to a. portion ofthe frequency spectrum occupied by a sideband of saidamplitude-modulated video componen-ts, comprising selectively receivingsaid carrier Wave, detecting said frequency variations of said carrierwave to derive said synchronizing components, detecting said amplitudemodulation of said carrier to derive said video-signal components, andutilizing said derived components to reproduce the transmitted program.

28. 'Ihe method of receiving and reproducing a television programtransmitted by a. carrier wave normally of a predetermined frequency buthaving its frequency varied in one or more successive cycles of onepredetermined frequency during line-retrace-scanning periods and variedin one or more successive cycles of a different predetermined frequencyduring successive fieldretrace scanning periods and amplitude-modulatedby video-signal componentsduring tracescanning periods, comprisingselectively receiving said carrier wave, detecting said amplitudemodulation of the received carrier to derive said video-signalcomponents, detecting the frequency modulation of the received carrierto derive said cyclic frequency modulation, selecting said cyclicvariations of said one predetermined frequency to deriveline-synchronizing impulses, selecting said cyclic frequency modulationof said different predetermined frequency to derive field-synchronizingimpulses, and utilizing said derived video-signal components andsynchronizing impulses to reproduce the transmitted program.

29. A television signal receiver adapted to receive a modulated-carrierwave amplitude-modulated by vided-signal components during trace periodswhile its frequency is maintained constant during all of said traceperiods and frequency-modulated by synchronizing-signal components to apredetermined frequency deviation during retrace periods while itsamplitude is maintained constant during all of said retrace periodscomprising, means selectively responsive to said predeterminedcarrier-frequency deviation for deriving synchronizing-signalcomponents, means for amplitude-detecting said carrier wave to derivesaid video-signal components, and means for utilizing said derivedvideo-signal components for reproducing the transmitted program.

30. Atelevislon signal receiver adapted to receive a directly radiatedmodulated-carrier wave amplitude-modulated by video-signal componentsduring trace periods and frequency-modulated by synchronizing-signalcomponents to a predetermined frequency deviation during retrace periodscomprising, means frequency-selectively responsive to said predeterminedcarrierfrequency deviation for deriving synchronizingsignal components,amplitude-selective means coupled -to said frequency-selective means forselecting only amplitude values above a predetermined value iorsynchronizing an operation of said receiver, means foramplitude-detecting said carrier wave to derive said video-signalcomponents, and means for utilizing said derived video-signal componentsfor reproducing the transmitted program.

ARTHUR V. LOUGHREN.

CERTIFICATE 0F CORRECTION.

Patent No. 2,2 ,11.55; September 2, lSLLl.

ARTHUR V. LOUGHREN.

It is hereby certified that error appears in the printed specificationofthe above numbered patent requiring correction asfollows: Page 1,first column, line 14.7, for "increase" read --increases-; and secondcolumn, line l0, for "compounds" read -components; page Lp, firstcolumn, line 20, for "later" read--lation; page 5, first column, line 8,beginning with the words I'The cycles? strike out all to and including"duration." in line l5; page?, first column, 11n@ 52, for "that" readtn1s; line 6o, claimi, strike out and"; page 9, second column, line 65,claim 20for "transmitteing" read --trananitting--i and that the samLetters Patent should be read with this correction therein that the samemay conform to the record of the case in the Patent Office.

Signed and sealed this 5rd 'day of March, A. D. 19142.

. Henry van Arsdale, (Seal) Acting Commissioner of Patente.

